1. Field of the Invention
The present invention relates to an arrangement in a gamma unit, comprising a large number of radiation sources mounted within a radiation shield and having beam channels directed radially from said radiation sources toward a common focal point, said radiation shield comprising a space adapted to accommodate the head of a patient resting on a support.
2. The Prior Art
Gamma units of the above-mentioned type are previously known from, for example, ACTA RADIOLOGICA; Vol. 13:1974, "Irradiation of small structures through the intact skull", ACTA RADIOLOGICA, Vol. 14:1975, "Destruction of small intracranial tumours with .sup.60 Co gamma radiation" and JOURNAL OF NEUROLOGY, NEUROSURGERY & PSYCHIATRY, Vol. 46:1983 "Stereotactic Radiosurgery".
In the prior art arrangements, the center axis of the central member makes an angle of 55.degree. with the patient's longitudinal axis and the horizontal plane, and the beam channels have a varying distribution in respect of both position and number about this center axis. In known and planned gamma units, the beam channel distribution has varied between .+-.30.degree. to .+-.51.degree. in one plane and about .+-.80.degree. in the other. In these prior art arrangements, some beams will approach the longitudinal axis of the patient so that there is a certain risk that scattered radiation and an occasional primary beam will reach the surroundings when the door toward the central member is opened.